convert your non yics engine to a yics, 20 minute job

for you that have the non yics xj's here is the site for the instructions

http:home.westman.wave.ca/~jbe/YICS.htm

(info at end of tex)
I did this mod and it works, my engine does not spit back on cold starts, has a much smoother transition from off idle and was able to lower the idle rpm to a rock solid 1000 rpm.
parts required: 3/16 vacuum hose (enough to tee back to fuel valve)
three 3/16 brass or plastic tees.
Tie all vacuum ports together with tees and tubing and back to the fuel valve vacuum port.
cheap mod for improving performance.

 

Here's my "How to convert your YICS engine to a non YICS engine."

Insert your YICS tool in the YICS slot.
Do not remove.
Ride forever.

Or better yet, throw away your YICS tool and tune your bike without it.

 

Good article on making a YICS tool.

Completely out to lunch on what YICS is and does.

It is not a vacuum balancing system. If your bike is non-YICS, joining up the intakes will not make it a YICS motor, since you will not have the ports that are cast into the cylinder heads. YICS is NOT about balancing vacuum across the carbs. It is made to promote swirl inside the combustion chamber by admitting a jet of high speed fuel and air into the port through a specially cast hole in the cylinder head near the intake valve.

Not saying you haven't improved your performance, but it is not what YICS does.

 

YICS was primarily a fuel-efficiency enhancement. It does increase power, that's why you get the same amount of HP out of a YICS engine as a non-YICS engine, but with better fuel mileage.

 

Raises one very obvious question; I would think ...

If it were a good idea to the Mod; then why didn't the Engineers connect the Vacuum Ports at the Factory?

B _ D _ D E _ (Hey, Vanna ... give them a couple of Vowels)!

 

I don't know about you, but I work on cars for a living. from what I've seen most stuff the engineers come up with is usless, doesn't work right, and usually put in a pain in the butt spot. Granted they do come up with some good ideas. but man sometimes you just want to slap them silly.

Sorry that's my 2 cents worth.

 

And if YICS was such a great idea that "increases power and efficiency" (same with Suzuki's TSCC idea), how come they don't use it anymore??

Just 80's gimmicks, methinks....

 

Bad idea or not my bike performs much better
But you are right it will not be A yics system after the mod, My mistake.
Do you know if the yics system is still being used or how long it was in production.
wrenchmaster

 

I tried connecting the vacuum ports together like that once to see what would happen but couldn't tell any difference. I don't think the little ports are big enough that connecting them will make any difference.

 

My bike has always had A very light stumble from idle to off idle even after carb rebuild,color tune, synchronization ,new oem coils and all electrical connections cleaned. When I hooked up all the vacuum ports the stumble went away. It was very noticeable.
Could be it helped the idle mixtures some what, I know my settings are not to perfection. Any way I am enjoying the smooth transition.
wrenchmaster

 

>My bike has always had A very light stumble from idle to off idle...
You probably need to adjust the pilot jets but if that fixed it and you don't have to go through emissions every year then you should be in good shape.

 

Do you mean replace them with A different size?
I am running A K&N air filter with the stock air box, Macs 4 into 2 exhaust and all jets are stock.
would you have A suggestion on pilot jet size?
BTW I do not have pass emissions here in Hampton Ga
wrenchmaster

 

usually with the k & N filter and aftermarket exhaust you have to move your jet sizes up. I'll try to find the site I was on but it gave you a formula on what jet sizes to use when changing parts.

 

Isnt that exactly what they did when they made the yics system. I know that no one has a better idea than a 1981 Yamaha engineer. :roll: It really gets on my nerves how you will be the first one to berate someones idea without trying it.

 

Tying all the vacuum ports together might very well give a better idle, as wrenchmaster's results show. Especially on a bike which may have a bit of an off-synch condition, as there is no place within a NON-YICS engine where all 4 intake tracts can share vacuum from. Tying the four intake tracts together kind of gives a "poor-mans" synch to the engine.

YICS bikes, on the other hand, share vacuum all the time. That's ONE OF the results of have that YICS passage in the cylinder head.

The OTHER result, and the one that Yamaha talks about ad nauseam in their technical manuals in regards to the YICS system, is that the YICS port that GOES UP INTO THE CYLINDER HEAD, and THEN INTO THE COMBUSTION CHAMBER, and fires a small charge of air/fuel mix into the cylinder in a "rotational" orientation, is really the main design feature of the yics system. They claim it adds slightly to cylinder filling and helps to agitate the fuel mixture within the combustion chamber slightly, or at least enough to make a difference.

Which it probably does. ANYTHING that can be done to increase cylinder filling will result in more power. If you then LEAN out the fuel mixture slightly.....you know, IN EXACTLY THE WAY THAT THEY DID WHEN THEY WENT FROM A NON-YICS TO A YICS ENGINE, WHILE EVERYTHING ELSE STAYED THE SAME ('80-1 650 non-yics engines used #50/#195 air jets, while the '82-up 650 yics engines used #50/#205 air jets, about a 5% increase in the pilot air jet size, meaing at least a 5% leaner mixture)....then as result of drilling those holes, etc. they could run a 5% leaner mixture, meaning 5% greater fuel efficiency, and produce the same amount of power.

 

Regarding jet sizing:

Here is the info regarding jetting that I found:

1 jet size for custom 4 into 2 exhaust

2 jet sizes for 4 into 1 exhaust

1 jet size for K&N filter (single inside airbox)

1 jet size for drilling out the bottom of the airbox

2 jet sizes for both single K&N and drilled airbox

2 jet sizes for individual filters

2 jet sizes for no muffler (open header)

1 pilot jet size for every 3 main jet size increase

Add up all the jet size increases and subtract one. (Remember
they go in steps of 2.0 for each jet size)

Under a mismatch condition, like individual filters and stock
exhaust or 4 into 1 header with stock filter and air box, subtract
an additional 1 jet size.

Check plug color often, sync carbs after each jet change,
make sure the floats are set correctly, and seriously consider
purchasing a Color Tune.

Make sure your carbs are in perfect working order before
making jet changes.

Additional info: Decrease main jet size one step per
2000' above sea level. Decrease pilot jet every 6000'
above sea level.

--------------------------------------------------------------------------------
EXAMPLE:

Stock = 120 Main and 40 Pilot with Y-13 Needle

4 into 1 with Supertrapp = +2 Sizes Main Jet
K&N Pods = +2 sizes Main Jet
Subtract 1 = +3 Sizes Main Jet or a 126
Subtract One More Size for Altitude of 2500' Average

I figure a 124 Main and 42 Pilot should do the trick after adjustment.

**************************

Just be aware that the issue that most affects jet sizing is the restrictiveness of the INTAKE air flow, which is via the stock airbox/filter combination. Changing the air flow on the INTAKE side of the engine requires much more of an increase in fuel delivery requirements (jet size) than it does versus merely changing the EXHAUST flow by itself; doing both changes together may or may not have "additive" effects, depending on just how restrictive the aftermarket exhaust system is----and especially, at what RPM range(s) does that restriction occur at? Not all aftermarket exhaust systems are THAT much less restrictive than the stock factory 4-to-2 system.

The 650 K&N filter probably passes more air than the stock paper filter, although the 650 K&N filter is a TINY little filter for some odd reason, so the reduced (like, about 50% reduced) surface area of the K&N filter versus the stock paper filter may negate some of the "freer flowing" aspects of the K&N filter----which is why many people say that you don't have to re-jet the carbs due to ONLY a change to a K&N filter element in the 650/750 models. Changing to POD filters, on the other hand, basically means you're going to have to change jetting, no ifs, ands, or buts about it.........

The only way to know for sure is to read the plug insulators under various conditions....idle, crusing, heavy throttle, cold outside, warm outside, etc. A real pain in the rump, which is why most people don't do it, or do it improperly, and end up with all sorts of performance-related issues when going from stock to "some other" configurations. And the worst condition of all to end up with is a lean fuel mixture condition, especially at a typical crusing or bike usage rpm range, which can quickly eat up your engine, perhaps not all the way to catastrophic failure conditions, but enough to cause greatly increased heat and this rapid piston/cylinder/valve wear, and thus decreased engine performance, and do so over a remarkably short time span.

 

Cylinder head/combustion/fuel metering technology has come a LONG way since the 80's. Fuel injection, all by itself, makes a huge difference, with the precision that it affords. Cylinder head, combustion chamber, piston crown, intake port, camshaft lobe features and various other design elements make huge differences......consider, for a moment, that the highest paid (and most desired) people in the high-po engine design business (racing) are the cylinder head and cam designers/builders/tuners.....

In the 70's and 80's, the max compression ratios you could run "on the street" was 10 or 11:1, and that was on better gas than is available now. Hi-po engines of today run 11:1 or better all day long, on fuel that is remarkably lower octane. Why? Better cylinder head/combustion design is the primary reason. And, much better fuel efficiency for the power produced......and remember, all other things being equal, better fuel efficiency is a RESULT OF higher power output. Burning more OF the fuel introduced into the cylinder is the key to power output.

The "shortcut" way to more power is simply stuffing more fuel into the cylinder (richer mixtures), which is certainly easier to do, but has its own set of drawbacks in the process of doing so.

 

Thanks Chacal for finding that thread. Hey Gearhead no need for looking up that thread but thanks for the offer.
I love this forum.
BTW Chacal thanks for the support and the information, that explains the YICS system very well.
wrenchmaster

 

i think i might try this vacuum connect mod tomarrow i will report findings.
i am always looking for better fuel efficiency.

 

Wrench, you're very welcome!

Blue.....let us know, although again, tying those vacuum ports together may make your bike idle/off-idle performance a little smoother, but it's questionable whether it will result in better fuel efficiency. Tying the ports together gives you a "backyard, all-of-the-time" synch effect (sounds good on paper, but it's the wrong way to accomplish a synch for a variety of reasons). YICS promotes combustions chamber filling/mixing, and that's where the additional power comes from. Synching and cylinder filling are two different (and here's a monkey-wrenchmaster in the works for you!: "but inter-related") things............